This invention relates to a method and apparatus for regulating combustion in a furnace or the like which is supplied with combustion air by means of a fan or blower and wherein the fuel supply is regulated according to the load.
It is well-known that in furnaces or boilers operating under varying load conditions the combustion air supply thereto can be controlled by dampers or the like which are adjustable. Moreover, in the case of oil burners it is the normal practice to supply air to an atomizing zone by means of a fan which is driven by an electric motor running at a constant number of revolutions per minute irrespective of the load and therefore irrespective of the amount of fuel supplied. The same is true in furnaces using other fuels, i.e., the combustion air is supplied by an essentially constant speed blower. Under these circumstances the amount of electricity consumed by the blower will be constant and independent of the load. The consumption of electricity will thus be unnecessarily large at low loads, and it is to be noted that in these prior art systems no allowance has been made for variation in the caloric value of the fuel or the pressure and temperature conditions of the air.
Another known technique for combustion control utilizes a step-wise form of regulation of the rotational speed of the blower to control the amount of combustion air being supplied. When this technique is used, the actual variation of the blower speed generally lags a change in condition by a significant amount of time, and in fact, the lag may be so great the the change in blower speed does not truly correlate with the current operating conditions. That is, another change in operating condition may have occurred by the time a change in blower speed is effected to correspond with a preceding change in operating condition. Thus, it is not at all unusual in this type of combustion control system for the adjustment of the blower speed not to correlate with the current actual operating conditions.
Another prior art technique is found in German Pat. No. 490,291; this technique contemplates providing an infinitely variable adjustment for a blower and a fuel pump so that the amount of air and fuel supply to the furnace correspond with varying load conditions. Quite clearly, this technique is far superior to the aforementioned means for combustion control insofar as there can be a relatively high degree of operating efficiency at various stages. However, it is important to note that in this system the air supply is neither corrected according to specific air conditions nor for the caloric value of the fuel being used. When there are changes in the latter conditions, the actual operating conditions can be far different from the optimum. In employing this particular technique there is a risk that although the furnace is operating properly, it at all times will be wrongly adjusted for all load conditions, because the actual conditions of fuel and combustion air are being ignored. For example, this can happen if the atmospheric pressure is unusually low.
It is, therefore, an object of this invention to provide a means and method for controlling the combustion in a furnace by controlling the supply of combustion air to the furnace by means of an infinitely variable adjustment of the rotational speed and/or fan blade angle of a blower which adjustment takes into consideration the actual condition of the fuel and air being supplied to the furnace.
Another object of the invention is to provide a means and method by which the rotational speed of a blower supplying combustion air to a furnace is controlled in accordance with the oxygen or carbon dioxide content of flue exhaust gasses and wherein the aforesaid blower speed continuously bears the prescribed relationship to the current condition of the flue gasses.
Still another object of the invention is to provide a means and method for regulating combustion in a furnace wherein the rotational speed of a blower supplying combustion air to the furnace is additionally controlled in accordance with the pressure and temperature conditions of the air being supplied as combustion air and the caloric values of the fuel being used.
A further object of the invention is to provide means and method for controlling the combustion in a furnace wherein the rotational speed of a blower supplying combustion air to the furnace is controlled to bear a prescribed relationship to the amount of fuel currently being supplied, and wherein the current rotational speed of the blower bears the prescribed relationship on a continuous basis.
An additional object of the invention is to provide a means and method for regulating the combustion in a furnace wherein the oxygen or carbon dioxide content of flue exhaust gases are continuously measured and wherein the amount of fuel supplied to the furnace is being continuously measured and wherein the rotational speed of a blower supplying combustion air to the furnace is continuously adjusted on the basis of the continuous measurements of flue gases and fuel.
Another object of the invention is to provide a primarily electronic apparatus for regulating the combustion in a furnace which meets the foregoing objects while rapidly providing the continuous, infinite variations described hereinabove.